1. Field of the Invention
This invention relates to the production of cellular vitreous slabs or shapes having a substantial part of the volume composed of gases enclosed in the cells, and is particularly concerned with the process and apparatus to produce cellular vitreous refractory material in prescribed shapes and products therefrom of lighter densities then conventional brick or tile, and more impermeable.
2. Description of the Prior Art
There is one commercial producer of cellular glass blocks who uses a process in which powdered or pulverized glass is the main raw material. The fine particle size glass powder is mixed with two chemical agents which react to form gas at a temperature above the point where the glass sinters to seal in the gas. The same corporation owns U.S. Pat. No. 2,890,127 which discloses using powdered quartzite as the charge and discrete carbon particles or silicon carbide, the carbon reacting with SiO.sub.2 to produce the foaming gas. It also owns U.S. Pat. No. 2,890,126 which discloses supporting the charge by graphite slabs and the addition of compounds, such as feldspar, to the mixture of U.S. Pat. No. 2,890,127 to decrease viscosity and improve sintering and cellulation. Commercial production was maintained intermittently for several years and then abandoned. These two patents pointed out the radically improved properties obtained when the glass blocks are of almost pure silica glass.
The kiln for the above described commerical process was made of graphite slabs which acted as resistance heaters. The charge was carried in graphite pans pushed in a train through the kiln. The process was not successful, as I understand the matter, because it was too expensive and the graphite slabs and pans would not last. My process avoids expensive grinding to fine particle size and the use of expensive high quality graphite for kiln parts and charge pans.
Various patents describe the foaming of various minerals to avoid the expense of first making powdered glass. None have resulted in a sustained commercial production of a slab or shape; however, Dow Chemical did produce "market development" quantities of foamed vitreous clay blocks for several years, using clay as a raw material. The prior art of bloating clay into lumps of cellulated material gave Dow the hot lumps which they pressed and thus welded into blocks.
For centuries, prescribed shapes of roof tile, wall tile, floor tile, brick, and various ceramic bodies, such as flower pots, china and the like, have been produced by pressing a mixture of clay and water then drying and sintering the same. Such products as bricks have been produced by extruding the clay mixtures so as to compact the charge into quite dense masses. "Dry" pressing of the clay mixture at high pressure has also been employed, extensively.
Such dense clay mixtures produced by dry pressing or damp pressing have usually contained from about 5% to 8% moisture and have been subjected to from about 1000 psi to about 5000 psi. In the prior art extrusion of clay mixtures, the moisture content of the clay mixture is usually higher, namely in the neighborhood of from 15% to 20%, however, very substantial pressure is still necessary.
Each of the resulting dense mixtures must be dried quite slowly over an extended period of time so as to permit the gradual migration of the moisture through the clay. If such a procedure is not followed, the clay may crack or explode during drying. The resulting sintered clay is quite dense and holds its original shape without cracking or crazing. The sintering is at a temperature below the fusion temperature of the clay which is employed. I use a mix which is low in moisture and is pressed at low pressures. This enables the rapid heating of the charge which may crack on sintering but such cracks are later healed.
In the past, the cellulation of clay materials have been carried out. For example, Ford, In U.S. Pat. No. 2,485,724 taught that by using flux, low temperature foaming of a special Albany slip clay could be carried out using an oxygen containing agent and carbon in the form of carbon black. Ford also taught that urea, sugar, dextrose or molasses could be substituted for the carbon black to produce bodies having densities of from 10 to 20 lbs. per cubic foot. The firing temperature was in the neighborhood of 1500.degree. F. to 1800.degree. F.
In my U.S. Pat. No. 3,967,970 I produced a bloated clay by firing at about 2100.degree. F. to 2300.degree. F. of a mixture of clay, sugar or urea, sodium or potassium hydroxide and water. In example 4 of that patent, I substituted trisodium phosphate for the sodium hydroxide.
The process of the present invention eliminates the expense, trouble and hazards of using a flux and has thus produced a foamed product having a higher melting point and more resistant to water and chemical agents.
U.S. Pat. No. 2,337,672 discloses the manufacturers of multicellular glass by heating a charge from glass, oxide of arsenic, zinc or cadmium and carbon powder to produce a reaction between the oxide and the carbon.
Other less pertinent U.S. patents relating to bloating of ceramic material include the following:
______________________________________ 3,174,870 3,150,988 3,666,506 2,880,099 3,536,503 2,564,978 3,307,957 2,670,299 ______________________________________
None of the prior art patents discussed above disclose any practical means for producing a foamed mineral block or plate quickly and economically.
Accordingly, it is an object of the present invention to provide an apparatus for and method of producing a foamed mineral artical quickly, efficiently and at a low cost.
Another object of the present invention is to provide a foamed mineral article which is highly insulative and light weight and yet is resistant to aging, corrosion and water absorption.
Another object of the present invention is to provide a process and apparatus for producing a foamed mineral material and the material, itself, which has a high structural strength capable of forming load bearing walls and roof decks with wide spaced supports and can be produced in large sheets.
Other objects features and advantages of the present invention will become apparent from the following detailed description.